The researchers followed more than 9,000 females, beginning when
they were aged 9 to 15 in 1996, until 2010, when they were young
women. Eating peanut butter three days a week reduced the risk of
developing benign breast disease by 39 percent, said Dr. Graham
Colditz, senior study author.

"I think this gives us enormous hope there are strategies we could be following to help prevent breast cancer that we haven't capitalized on yet," said Colditz, the associate director for cancer prevention and control at the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine, in St. Louis.

The study, published online Sept. 17 in
Breast Cancer Research and Treatment, was funded by the
Breast Cancer Research Foundation and the U.S. National Institutes
of Health.

Benign breast disease is fairly common, and a known risk factor
for breast cancer, Colditz said. Before menopause, "about one in
four women have a benign lesion, confirmed by biopsy," he said.
"It's very clear there is a strong link between the benign lesion
and the subsequent risk of invasive breast cancer."

Depending on the characteristics of the benign lesion, he said,
benign breast disease could increase breast cancer risk by
threefold.

The study participants were part of a long-term, ongoing study
on the health effects of diet and exercise in young people. They
filled out questionnaires about their diet annually from 1996 until
2001, then four more times until 2010. They also reported if they
had been diagnosed with benign breast disease. In all, 112 women
said they had.

The researchers looked at foods with vegetable protein and
vegetable fats, then focused on individual foods, including peanut
butter, peanuts or other nuts, beans and corn.

A daily serving of any of these foods was linked with a 68
percent reduced risk of benign breast disease. At age 14, a daily
serving of any of those foods was linked with a 66 percent lower
risk of benign breast disease, and girls who had about three
servings a week of peanut butter had a 39 percent lower risk.

The researchers found a link between eating peanut butter and
lower breast disease risk, not a cause-and-effect relationship, and
Colditz said he can't explain yet why the peanut butter seems
protective.

"It could well be the protein," he said. In previous studies, the researchers have looked at other factors of a healthy diet, such as milk consumption, and their role in breast health. The peanut butter finding, he said, is strong, even when taking into account an overall healthy diet. "It's not something we can make go away," he said.

For now, Colditz said, the take-home message is for teens and
preteens to substitute peanuts and peanut butter for less-healthy
snacks such as cookies.

Another expert who reviewed the findings said the study is well
done.

Dr. Steven Chen, an associate clinical professor of breast and
endocrine surgery at the City of Hope Comprehensive Cancer Center,
in Duarte, Calif., said that while lowering benign breast disease
does lower breast cancer risk, many other factors increase breast
cancer risk besides benign breast disease.

"It's always good to lower any risk [of breast cancer] you can, but whether peanut butter intake will have a major impact on developing breast cancer down the line, only time will tell," Chen said.

As for how to explain the link? "It's hard to say at this
point," Chen said, adding that in countries where less meat is
eaten, less breast cancer risk is reported. Based on the study
findings, he said, teen girls and preteens "shouldn't avoid peanut
butter and nuts if they are not allergic." Getting some protein
through vegetables, which was also looked at in the study, is a
good idea, too, he added.

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